I’m currently a new first year Stony Brook student and while my move in was good, I continue to have a reoccurring feeling that this school was not the one meant for me. I think the majority of the reason as to why I feel this way is because my sister went to Notre Dame, and I wanted to have that same picture perfect experience as her. I didn’t get in to Notre Dame and Stony was my cheapest option. Other schools wanted me to pay $40K+ and to me, that’s not worth it. Any advice to ease the tension/actions I should take?
Throw yourself into it. If you don’t, it will almost certainly be the wrong place! Get involved in things that interest you. Find your people.
Make sure you get good grades. In winter, reassess how you’re feeling. If, in spite of your best efforts, you want to consider transferring, you can start then. Your good grades will help.
It’s still early. Honestly, even ND would probably feel unsettled right now. This is a big, challenging transition. Don’t be too quick to judge.
You chose your school for sound reasons, and you just got there. You are dwelling pointlessly on your sister’s experience. Dwell on making the most of YOUR experience. Stony Brook is a good school. Smart people are there. You will have a great college experience if you involve yourself in campus life and have reasonable expectaitons about the time it takes to adjust to college. Expect things to feel more normal by November. If it happens sooner, that’s a bonus. Ittake slime, whihc you can’t rush, to get settled and meet new people. If you think it’s a lost cause by the end of October, make plans to transfer.
You got into a top notch public university and won’t pay an arm and a leg for it. Congratulations on both fronts!
Now, make the best of it: join study groups and clubs, go to office hours (with questions based on lecture or textbook at the ready), make sure you have at least one class with 25 students or fewer. 
Give it time. Finish the year before making any rash decisions.
Don’t try to replicate your sister’s college experience – go out and make the most of your school. Stony Brook is a very fine school, especially in the STEM fields. Meet people, get involved in clubs that interest you, get to know your professors and create your own college experience.
I agree with the other posts above. You are at a great school. It is perfectly normal to feel nervous at the very beginning of your first week there. Over time you will get to meet future friends and find things that you like to do and find your way around the school and have a chance to do very well. Your reasoning regarding why you choose this school is sound and very sensible.
There might be a bit of “the grass is always greener somewhere else” going on. However, there is no perfect school. You are at a very good one. As @happy1 said “go out and make the most of your school”. Good luck and best wishes.
What a top value school! You can shine there!
A lot of us attend our second choice schools, often for financial reasons. So know that you’re surrounded by tons of really smart people who purposefully chose Stony Brook for the money - wise of you all.
That said, if you go into this thinking that Stony Brook is a poor second choice to Notre Dame, it will be one. But if you really try to make a go of things at Stony Brook, the place may shock you. You may end up loving it (as I did my second choice school, which - like you - I attended for financial reasons.) So join clubs and activities and do more than just show up for meetings - volunteer to do what needs doing, and really get involved. Find out who the best professors are on campus, and take classes with them. Do an independent study with your favorite professor. Get involved in a professor’s research. Do a national or international student exchange. Join the honors program, if you qualify. Do an internship someplace fabulous. And see where it all takes you.
It’s actually pretty normal to have nerves right now, and to be second guessing. In consumer behavior, it’s called “buyer’s remorse”, and it’s 100% normal. It will pass as you adapt to campus life. If it does not - if, at the end of this term, you find you don’t like SB, then you can look at your options. But for now, throw yourself into the place and see what happens.
I think the media narrative about college is probably pretty damaging to most people, but the truth is, there’s no one good way to have a college experience. If you spend too much time focusing on your sister’s experience and your disappointment over not having hers, you’ll miss your opportunity to craft your own experience that will be just as good or better. It’s a great university; the campus is beautiful; you’re probably 2-2.5 hours away from Manhattan by train; it’s a pretty diverse place to go to college; your classmates will be bright students who were generally in the top quarter of their high school class (and almost half were in the top tenth).
Throw yourself into everything, and get involved in the things you like. Look for friends and make sure that you make efforts to connect with others.
Comparison causes misery and ruins relationships. You have a great school and will be able to graduate in much better financial condition. This is something you will appreciate for years! Jump in and enjoy your school.